1. Field of the Invention
The preset invention relates to a production system including a machine tool and a robot configured to supply and eject a workpiece processed by the machine tool.
2. Description of the Related Art
In a system including a machine tool and a robot configured to supply and eject a workpiece processed by the machine tool, when a positional displacement of the robot relative to the machine tool occurs, the robot cannot carry out an operation thereof precisely. Therefore, it is desired that the positional displacement is measured and corrected appropriately.
As relevant prior art documents, JP 2009-000782 A discloses a robot control system including a robot having a robot arm and a robot hand with a chuck for gripping a workpiece, attached to a front end of the robot arm; an operation section carrying out teaching input for the robot; a camera section capable of capturing the workpiece; and a control section which corrects a given coordinate position taught to the operation section based on an image captured by the camera section and drives/controls the robot so as to move the corrected coordinate position.
Further, JP S62-191904 A discloses a position correcting method used when a robot mounted on an unmanned carrier is conveyed to an operation position and an operation is carried out for a workpiece located at the operation position based on a previously taught teaching point. In the method, a predetermined portion is marked at the operation position, the position of the mark is detected by using a detecting means of the robot, and the position of the teaching point is corrected based on the detected position of the mark and the taught position of the mark.
In a system including a machine tool and a robot, the machine tool and the robot may be fixed to a floor by using an anchor bolt, etc., so that the placement positions of the machine tool and the robot are not displaced during operation of the system. However, when the machine tool or the robot is shifted (for example, a layout of the factory should be changed, etc.), it is necessary to refix the machine tool or the robot with an anchor bolt, etc., which is very troublesome. Therefore, when the layout is often changed, it is preferable that the machine tool or the robot is simply installed by using an outrigger, etc., without being fixed to the floor by using an anchor bolt.
However, when an outrigger is used, the placement position of the machine tool or the root may be gradually displaced due to vibration of the machine tool during operation or the motion of the robot arm, etc., whereby the positional relationship between the machine tool and the robot may be changed. When an amount of change in the positional relationship exceeds a certain level, the workpiece cannot be attached (or supplied) to or detached (or ejected) from the machine tool by the robot. In such a case, a camera is attached to a front end of the robot so as to detect the position of the workpiece and the position of a jig to which the workpiece is attached. By virtue of this, even when the placement position of the machine tool or the robot is displaced, the operation position of the robot is corrected based on the detection result, so that the robot can supply and eject the workpiece.
However, in the prior art, it is necessary to supply or eject a workpiece after the position of the workpiece or the jig is measured by the camera, and thus it takes time to supply or eject the workpiece. Further, when the workpiece or the jig to be measured by the camera is positioned inside the machine tool, it is difficult to properly measure the position thereof since the camera is affected by cutting oil.
For example, in JP 2009-000782 A, by capturing the workpiece by the compact camera arranged on the front end of the robot arm, the taught coordinate position can be corrected based on the image obtained by the camera and the robot can be moved to the corrected coordinate position. However, since the robot is moved to grip the workpiece after the workpiece is captured by the camera, the robot cannot be moved during the camera captures the workpiece and/or during the obtained image data is processed, whereby a cycle time of the robot is extended. Further, when the workpiece is supplied to or ejected from the machine tool, it is necessary to move the robot arm into the machine tool and move the camera close to the workpiece to capture the workpiece, and thus the camera is likely to be affected by cutting oil.
On the other hand, in JP S62-191904 A, the robot mounted on the unmanned carrier is moved to the operation position so as to carry out operation for the workpiece located at the operation position. In this regard, the predetermined portion is marked at the operation position, the position of the mark is detected by using the detecting means of the robot, and the difference between the detected position of the mark and the teaching point is detected, whereby the teaching point of the robot can be corrected. However, in this technique, the mark is detected after the unmanned carrier is moved to the operation position, and the position of the teaching point of the robot is corrected after the relative position. Therefore, in JP S62-191904 A, the correction of the displaced position is not discussed or considered when the same operation is repeated at the same position.